The atomic and molecular interactions which specify the architecture of the oncornavirus RNP-complex will be elucidated by: 1) determination of the complete primary and secondary structure of AMV p12; 2) comparative sequence studies of avian oncornavirus p12 and mammalian oncornavirus p10; 3) chemical modification of p12 in the intact RNP-complex and after purification under nondenaturing conditions; 4) cross-linking of p12 in the intact RNP-complex with bifunctional reagents; 5) examining the interaction of p12 with homologous and heterologous virus specific RNAs and with nonviral nucleic acids; 6) reconstitution of the RNA-p12 complex and 7) determination of the three dimensional structure of AMV p12 by X-ray crystallography. The chemical basis for the biological specificity of different avian virus subgroups will be elucidated by: 1) chemical analyses of gp85s isolated from subgroup A, B and C viruses; 2) studies of the architecture of the virus surface projections using bifunctional reagents; 3) studies of the interaction of purified gp85s and virus surface projections with cultured chicken cells by focus and plaque formation assays; and 4) isolation and characterization of specific host cell receptors for each avian virus subgroup.